The invention disclosed herein pertains to distillers for producing potable water from impure water.
Typical distillers used in residences for water purification comprise a boiler to which impure (raw) water is admitted from the water mains for being converted to steam. The heat for effecting conversion of raw water to steam is usually an electric heater element which, in some designs, is immersed in water within the boiler and in other designs is arranged in heat exchange contact with an external surface of the boiler. The generated steam is conducted from the boiler to the inlet of a steam condenser which is usually cooled externally by an air stream from a fan. Typically, the pure condensate is delivered to a storage tank. A motor-driven pump is usually present in the distiller assembly for delivering water from storage to a faucet on demand.
Residential water distillers can be technically quite sophisticated as is demonstrated in U.S. Pat. Nos. 5,110,419; 5,188,710; and 5,200,039 which are assigned to the assignee of this application and are incorporated herein by reference. The distillers described in these patents are adapted to perform a variety of control functions of which the owner does not have to be aware. An electronic controller, which may be based on a microprocessor, governs the functions. For example, a sensor such as a float switch signals the controller when the quantity of pure water in the storage tank is low, in which case the controller responds by switching the heater element on and, possibly, at the same time opens a raw water infeed valve and adds water to the boiler for being converted to steam. A sensor may detect the temperature of the heater element as a representation of the depth of water in the boiler so as to independently close the infeed valve or open it as required to repeat a steam production cycle. Data representative of the total run time of the distiller may be accumulated in an electronic memory which provides a signal to the distiller owner that certain maintenance steps must be taken such as removal of mineral deposits from the boiler-evaporator and/or the heater element.
Generally, existing distillers perform their functions in a pre-determined order. At start up, the heater element may be energized for a short time interval to bring the element or boiler up to near steam generating temperature. Next, raw water that is to be distilled and purified, is admitted to the boiler and, in a short time, generation of steam starts. Continuing evaporation of the water in the boiler results in a drop in the water level. The low level water condition is sensed and the response to the condition must be replenishment of raw water in the boiler.
A problem in pre-existing distillers is that precise correlation between boiler or heater element temperature and a demand for water infeed cannot be obtained. One of the reasons is that as long as there is some water in contact with the boiler body or with the heater element, the body or element tends to remain at the 212.degree. F. or 100.degree. C. of the boiling water. Hence, there is no sensible increase in the temperature of the heater element nor in the steam boiler body above the boiling temperature of water until the boiler or heater element becomes totally dry. Sensing of a temperature above the boiling point of water as an indication of the boiler having gone dry induces a controller to respond by opening a raw water infeed valve. The consequences are unfavorable. The first incoming quantity of raw water runs onto a surface that is significantly hotter than the minimum temperature that is necessary to generate steam. This results in the raw water flashing into steam with explosive force accompanied by a substantial increase in the steam pressure within the boiler. The pressure rise can be so rapid that the steam cannot be relieved fast enough to the condenser to avoid damage to the boiler and even to other parts of the distiller within the distiller housing. This problem and other problems in existing water distillers are eliminated by the invention disclosed herein. Whenever water boils vigorously, as it often does in the small boilers used in residential distillers, tiny microglobules of water characterized as mist, become entrained in and can be carried in the steam from the boiler. There is a probability of the mist or globules containing impurities because the water is just propelled out of the raw water in the boiler. Avoiding the steam flashing problem just discussed removes one cause of mist production. It is important to make sure that no impure carryover water in the form of mist or microglobules can ever reach the condenser and get into the distilled water storage tank. The invention disclosed herein solves this problem, too.